1. Field of the Invention
This invention relates to a catalyst for hydrogenating hydrocarbon oils. More particularly, this invention relates to a catalyst for the hydrogenation of hydrocarbon oils containing aromatic compounds. Still more particularly, this invention relates to a noble metal catalyst having a novel pore structure which exhibits a high activity for the hydrogenation of aromatic compounds in hydrocarbon oils and finds particular use in the production of jet fuel, kerosene and white oils.
2. Description of the Prior Art
Aromatic hydrocarbons contained in middle fractions such as jet fuel, kerosene and solvents, reduce their combustion characteristics as evaluated by the smoke point, the luminometer number and the wick-chair weight and also degrade the quality of middle distillate products. Especially in the case of white oils for industrial and pharmaceutical uses, a high quality hydrocarbon oil is required. Therefore, the presence of even minute amounts of aromatic hydrocarbons is not allowed. Further, lubricating oil fractions containing aromatic hydrocarbons are inferior in quality because the aromatics contribute to a low viscosity index and a high ultraviolet absorption.
Accordingly, hydrogenation is generally conducted for removing aromatic hydrocarbons contained in hydrocarbon oils such as middle fractions and lubricating oil fractions. Aromatic hydrocarbons are either converted to naphthenic hydrocarbons by aromatic nuclear saturation caused by hydrogenation carried out under considerably severe reaction conditions or they are hydrocracked to paraffinic hydrocarbons by such hydrogenation. In such hydrogenation it is necessary that only aromatic hydrocarbons be selectively converted. Some catalysts meeting this requirement have already been proposed, such as i.e., a catalyst composed of a noble metal of group VIII of the Periodic Table such as platinum and palladium, a catalyst containing a metal of group VIII of the Periodic Table and an oxide and/or sulfide of a metal of group VI of the Periodic Table, and a catalyst composed of reduced nickel.
In solid catalysts used in chemical reactions, the pore structure of the catalyst is very important, because it is instrumental in controlling the reaction site, and activity. More specifically, in solid catalysts, it is indispensable that (1) the catalytic reaction activity per unit volume should be high, (2) reactants should easily be transferred to active points. (3) the catalyst life should be long, and further, (4) the mechanical strength should be high enough to resist conditions in industrial applications. The pore structure significantly influences these properties required of catalysts.
However, the catalysts known in the prior art are defective in that either their activity for hydrogenating aromatic compounds is insufficient or they are readily poisoned by sulfur compounds contained in the hydrocarbon oils.